Safety device for rectifiers



0ct. 12, 1948. H. A. w. KLlNKHAMl-:R Erm. 2,451,095

Smm xmvrcn Fon nac'nrmns Filed April 25', 1946 WUI/7 645555 y ffArron/v51 1 Patented' oer. 1 2, 194s l -sAFE'rrv DEvrcE FoaaEcrrrIaasff- Hendrik Abraham Iwummill v'Inneneimer' ma Ewout Cassee,Eindhoven, Netherlands, assign..

ors, by meme-assignments, to Hartford Natlona Bank and Trust Company,Hartford, Conn., as

trustee Appuuon'Aprn 25. 194e; serial No. 664.722

Inj the Netherlands January 29, 1,942

section 1, Public' Law 69o, August s.' 194e A Patent expires' January29, 1962- reach the rectiflers by temporarily interrupting theconnection of the rectiflers to the supply transformer when the supplyvoltage is switched on. This interruption may be made into a constrainedcircuit arrangement by constructing the supply switch for example so asto comprise one pre-position in which the rectiilers are not yetconnected up on the transformer being con-` nected into the circuit. Inthis case, the safety device is, however, not effective if the supplyvoltage returns after a disturbance. It is more efficientV to arrangefor the interruption being effected automatically by a magnetic timeswitch Whose coil is connected for example tothe input terminal of thedevice. A disadvantage cf this construction consists-in that withsmaller rectiers the cost is proportionallyy comparatively high.

l If, however, a much less costly time lag relayv is used instead of themagnetic switch, the reliability of service is often-insufficient sincethe entire output has always to be supplied via the relay contact whichis constructed so as'to be much less sturdy than with a magnetic switch.

The invention provides a more profitable solution for safeguarding thedevice of the type mentioned in the opening part.

According to the invention, the detrimental voltage is connected to theseries combination of an incandescent lamp and switch.

It is known that generally the resistance of an incandescent lamp whenhot is a multiple of that when cold. According to the invention, thisproperty is made available for conducting away the occurring detrimentalvoltage viathe closed switch through a cold incandescent lamp which ispossessed of a low resistance in such manner that therectiers aresafeguarded against dam age to a satisfactory extent.' According as thefilament rises in temperature its resistance increases with the resultthat the voltage 'is supplied to the rectiflers gradually. It istherefore necessary for the lamp so to be chosen that its coldresistance is low enough to derive the detrimental voltage and that itsthermal capacity is device safe-V `e claims. (ci. irs-ac3) y high-enoughto ensure` a sufficiently long heating-up Vperiod and thus asufficiently gradual passage to the operating condition.

`With incandescent lamps normally obtainable commercially the ratiobetween the hot and the cold resistance is for example about 14, as islargely sufficient for the object aimed at.

After the voltage, has thus been supplied gradually tojthe rectiers thelamp is switched out by means'of the switch. In the first place aVcontinual 'load of the burning incandescent lamp which is no longereffective is thus avoided for example that the harmful voltage does notv and secondlyythe filament is restored to its cold state of lowresistance inl order thatl it may at .once act again for example aftertherectiiler system has been put out of use. In addition to the.desideratum that the lamp should take up asy little room as possibleand its cost should be a minimum preference should be given, in view ofthe said disconnection, to a lamp whose current vwhich the relay willhave to interrupt is so low that a relay of cheap construction maysuillce. 1

Further improvingl the device according to the invention by means of azero potential device by which the open switch is closed when the supplyvoltage falls out in an unexpected manner' has in addition the effect ofsafeguarding against detrimental voltages on the unexpected return ofthe supply voltage.

According to a further feature of the invention, the disconnection ofthe lamp after the termination of the heating-up period is brought aboutas quickly as possible. This ensures various advantages. In the firstplace, the running time` of the lamp is limited to a minimum so that thelife is prolonged. In addition, the time over which the lamp acts as aload is reduced as far asv possible so that the current losses remainlimited toA a minimum. Thirdly, the lamp can again act as a safetydevice within the shortest time possible and this is important if thesupply voltage would accidentally again be suppressed a short time afterthe' system has voltage that it is overloaded for a short time.

Thus, the cost is considerably reduced and shortening of the life hardlyoccurs in pratice.

Preferably, the disconnection is automatically effected by means of atime relay having a time constant of the order of magnitude of say from0.3 to 0.9 second. Even a cheap direct current y l #51.0951) UNiTED-s'lArrzs PATENT. OFFICE a Thus, the time over which 3 relay havingconnected in series with it a small blocking layer rectifier andconnected to any of the alternating voltages occurring in the circuitarrangement is generally serviceable.

Taking into account the above-mentioned points of view (sufficient lowcold resistance, sumciently high thermal capacity, small volume, lowcost, small current) it is possible to be guided by the followingconsiderations when selecting from the available type of incandescentlamps:

(a) The intersection of the current-voltage characteristic curve of therectifier with that of the cold filament should preferably have avoltage o! from 15% to 50% of the voltage to which the safety-circuit isconnected in normal use.

(b) The nominal voltage of the lamp should be a minimum but should notbe lower than of the voltagevto which the safety-circuit is connected innormal use.

The invention is particularly important -with transformer circuits inwhich particularly high voltages occur upon the network being switchedon. This may occur for example with transformer circuits whosealternating current part includes a condenser. Such a circuitarrangement is obtained inter alla if use is made of a saturated and anunsaturated transformer whose primaries are connected in parallel withthe supply circuit a condenser being connected in series lwith theprimary of the saturated transformer,

whereas the secondaries are connected to the rectifier in seriesconnection. The circuit described has been suggested before,particularly with the object of obtaining a voltage-current character-.istie curve a part of which is horizontal with comparatively low loads.and is comparatively steep with higher loads. Hence, in the case of alower load an essentially constant voltage and in the ease of higherloads a current limitation due to a rapid decrease of the voltage isobtained.

In addition, in this circuit arrangement there may occur with no-load orlow-lead rectifier the phenomenon not yet entirely explained that onswitching-on a voltage-current characteristic curve quite different fromthat previously desired makes its appearance either temporarily or moreor less stationarily, the voltage Ibeing found to have a considerablyhigher value. These' phe nomena, which may also give rise to damage ofthe rectiflers, are also rendered inoiensive by the use of theinvention.

In order that the invention may be clearly undcrstood and readilycarried into eiect it will now be described more fully with reference tothe accompanying drawing, in which several schematically representedforms of construction are illustrated.

Fig. 1 shows a rectifier I which is supplied from the secondary 2 of atransformer 3, the primary 4 being connected to the supply circuit 5.Interposed between the secondary 2 of transformer 3 and rectifier I is alter choke 2|.

According to the invention, the voltages occurring in the supply circuiton the supply part being switched on are conducted away with theinter-position of the series combination of an incandescent lamp 6 and aswitch 1 so that the rectifier I is safeguarded against said voltages,it being premised that the load s is capable of withstanding thesevoltages. If this should not be the case the right hand terminal of theincandescent lamp may be connected to the lowermost terminal of the loadso that both' the rectifier and the load are shunted by the incandescentlamp with switch.

4 After the lamp l is heated up and as a result thereof the rectifier Iis gradually connected to the operating voltage the switch 1 is openedby the relay coil I. For this purpose, a Gratz circuit -IU of smalldry-rectifiers with a resistance II connected in series therewith isarranged on the secondary side of the transformer. The rectined voltageis connected to the relay coil i and to a condenser I3. connected inparallel therewith through a switch I2.

Assuming the switches 1 and I2 to be maintained closed, for example bymeans of a spring, the condenser I2 will become charged with a certaintime lag across the resistance II on the network being switched-on. At agiven condenser voltage the relay coil 9 will be sufficiently energisedto open the switch 1 through which the detrimental voltages havemeanwhile escapedl Elther by mechanical coupling to the switch 1 or elseunder direct magnetic iniiuence of the coil 8 the switch I2 is alsoopened and connected to the resistance I5 via the contact I4, with theresult that the condenser I3 discharges rapidly. Thus thede-energisation time of the relay is maintained at a small value so thatafter a transient interruption of the network the relay is at once againcapable of switching on since so long as the supply voltage continuesthe switches 'I and I2 occupy the position described. As soon, however,as the voltage disappears, for example under the influence of adisturbance, the switch 1v is again closed, whereasthe switch -I2 bringsabout the parallel combination of the condenser I3 and the coil 8. Thedevice is thus again ready for use so as, on the return of supplyvoltage and thus of the voltages that may be,detrimental, to conductthem away across the lamp 5.

The following figures in which corresponding parts are provided withsimilar references still show some few diiferent constructions.

Referring to Fig. 2, the incandescent lamp with the switch are connectedto such a part of the secondary of the transformer system that thedetrimental voltage can be conducted away to a sumcient extent. Therectifier system is here constituted by a Gratz circuit I8 which issupplied from the two series-connected secondaries I1 and I8 of twotransformers I9 and 20. 'Ilhe primary 2I of the transformer I9 which isconstructed as a saturated transformer is connected to the supplycircuit in series with the condenser 22. The transformer 20 isproportioned to be smaller and unsaturated.

Referring to Fig. 3, the incandescent lamp 8 the direct currentside ofthe Gratz circuit II (Fig. 4) the incandescent lamp with the switch maybe connected to the direct current side of the rectiflers. In this casea comparatively large short-circuit current flows temporarily but thelatter is essentially in offensive for the rectifiers. The voltageswhich occur on the supply circuit being switched-on and-which aredetrimental are, however, prevented.

An additional advantage of the relay construction illustrated in Fig. 1consists in that the condenser Il need only be capable oi' withstandingthe attracting voltage of the relayand not the working voltage of thelatter since the condenser ilonly connected to the voltage during thetime Finally, when a battery is not provided on the direct current sideof the rectifiers, the supply of the relay may be connected to the saiddirect current side so that the rectifiers I can be omitted.

Although in the forms of construction given by way of example the seriescombination of incandescent lamp and switch is always used on thesecondary side of the transformer, this series combination may beconnected to the primary side in parallel AWith part of the whole of theprimary.

What we claim is:

1. In combination with an electrical supply system having rectifiermeans to which is applied a source of unrectified power, a safety deviceadapted to apply said power to said rectifier means at a predeterminedgradual rate, said safety device comprising an impedance having anonlinear temperature coeiiicient of impedance connected to said systemso as 'to absorb a portion of said power, the value of said impedancebeing low in the unheated state relative to the value in the fullyheating state, said impedance havingv a thermal capacity effecting theapplication of said power to said rectifier means at the desired rate,and switching means interposed between said impedance and said systemfor disconnecting said impedance after it has attained the fully heatedstate.

2. In combination with an electrical supply system having rectifiermeans to which is applied a source of unrectiiied power, a safety deviceadapt'- ed to apply the power to the rectifier means at a predeterminedgradual rate, said safety device comprising a lamp having anincandescent filamgent connected to said system so as to absorb aportion of said power, the resistance of said filament being low in theunheated state relative to resistance in the fully heated state, saidfilament having a thermal capacity effecting the application of thepower to the rectifier means at the desired rate, a normally closedswitch interposed betweensaid lamp and said system, and means responsiveto said power for opening said switch after said filament has attainedthe fully heated state.

3. In combination with an electrical supply system having rectifiermeans to which is applied a source of unrectified power, a safety deviceadapted to apply the power to the rectifier means at a predeterminedgradual rate, said safety device comprising a lamp having anincandescent filament connected to said system so as to absorb a portionof said power, the resistance of said filament being low in the unheatedstate relative to the resistance in the fully heated state, saidfilament having a thermal capacity effecting the application of thepower to the rectifier means at the desired rate, a normally closedswitch interposeii between said lamp and said system, a relay foropening said switch, a rectifier, said relay being connected throughsaidl rectifier to said source of power, and a condenser shunted acrosssaid relay, said condenser having a value causing said relay to beactuated at a time after said filament has attained the fully heatedstate.

4. In combination with an electrical supply system having rectifiermeans to which is applied a source of unrectified power, a safety deviceadapted to apply the power to the rectifier means at a predeterminedgradual rate, said safety device comprising a lamp having anincandescent filament connected to said system so as to absorb a portionof said power. the resistance of said filament being low in the unheatedstate relative to the resistance in the fully heated state, saidfilament having a thermal capacity effecting the application of thepower to the rectifier means at the desired rate, a first normallyclosed switch interposed between said lamp and said system, a rectifier,a relay connected through said rectifier to said source of power, acondenser, a discharge path for said condenser, and a second switch for5. An electrical supply system comprising a source of unrectified power,rectifying means, a transformer having a primary connected to saidsource and a secondary connected to said rectifying means, a .lamphaving an incandescent filament connected across said rectifying means,the resistance of said filament being low in the unheated state relativeto the resistance in the fully heated state, said filament having athermal capacity effecting the application of power to said rectifyingmeans at a predetermined gradual rate, a normally closed switchinterposed between said lamp and said rectifying means, a relay foropening said switch, a rectifier, said relay being coupled through saidrectifier to the secondary of said transformer, and a condenserconnected across said relay and having a value causing said relay to beactuated at a time after said filament has attained its fully heatedstate.

6. An electrical supply system comprising a source of alternatingcurrent, a saturable transformer having a primary and a secondary, anonsaturable transformer having a primary and a secondary, a condenser,said primary of said saturable transformer being coupled to said sourcethrough said condenser. said primary of said non-saturable transformerbeing connected to said source, rectifier means, the secondary of saidsaturable transformer being connected in series with the secondary ofsaid non-saturable transformer to said rectifier means. a lamp having anincandescent filament connected across a `portion of saidseries-connected secondaries. the resistance of said filament being lowin the unheated state relative to the resistance in the fully heatedstate, said filament having a thermal capacity effecting the applicationof power to said rectifying means -at a predetermined gradual rate, andswitching means interposed between said lamp andsaid secondaries fordisconnecting said lamp after said filament has vattained the fullyheated state.

HENDRIK ABRAHAM Y WIJNAND ELINKHAMER.

EWOUT CASSEE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,882,492 Edelmann Aug. 28. 19281,759,745 Grimditch.-.. May 20, 1930 2,209,948 Harmer Aug. 6. 1940

